Method and device for the generation of a plasma through electric discharge in a discharge space

ABSTRACT

The invention relates to a method and a device for the generation of a plasma through electric discharge in a discharge space which contains at least two electrodes, at least one of which is constructed from a matrix material or carrier material, such that an erosion-susceptible region with an evaporation spot is formed at least by the current flow. To present a method or a device for the generation of a plasma by electric discharge, it is suggested that a sacrificial substrate ( 38 ) is provided at least at the evaporation spot, the boiling point of said lying below the melting point of the carrier material ( 30 ), such that charge carriers arising in the current flow are mainly generated from the sacrificial substrate ( 38 ).

The invention relates to a method and a device for the generation of aplasma through electric discharge in a discharge space which contains atleast two electrodes, at least one of which is constructed from a matrixmaterial or carrier material, such that an erosion-susceptible regionwith an evaporation spot is formed at least by the current flow.

A plurality of such methods and devices is known. Thus WO-A-02/07484discloses a method and a device for the generation of short-waveradiation by means of a plasma based on a gas discharge, wherein besidesthe two plasma electrodes two further electrodes are used for apre-ionization. Apart from a complicated and accordingly expensiveelectronic control system for generating the plasma pinch, the fourelectrodes are to be additionally provided with cooling liquid forstabilizing the radiation source.

WO-A-01/95362 discloses a further device for generating a high-frequencyplasma pinch through electric discharge, wherein an electrode erosion isto be reduced in that electrical energy transmitted in resonance isstored back again between two capacitors by means of an additionalmagnetic switch that is in a saturated state. Lithium metal is presenton or within one of the electrodes in a further embodiment, whichlithium is evaporated by short laser radiation pulses of an additionallaser device so as to be excited in the plasma pinch for the emission ofextreme ultraviolet radiation. The energy of the laser radiation pulseincreases the thermal load of the electrode and further reduces itsoperational life.

Ignitrons, spark paths, triggered vacuum switches, or pseudo-sparkplasma switches used as switching elements in high-current pulsearrangements all comprise electrodes which have had an insufficientuseful life until now because of strong electrode erosion. The emissionof toxic combustion products of the electrode material, the formation ofozone, and/or ecological problems in the disposal of mercury from anignitron are particularly disadvantageous here for many fields ofapplication.

CH 301203 relates to an ignitron, for example with a sintered molybdenumsponge electrode for absorbing the mercury, which offers a highresistance to a discharge arc arising during switching. This ignitronhas only one sponge cathode in this case so as to provide an unchangingspatial relation to the cathode in all conditions of movement and ineach and every position of the ignitron with respect to an ignitor. Theuseful life of the electrode used as the ignitor, however, remains tooshort because of the erosion caused by the discharge arc.

Special electrode geometries are known from WO-A-99/29145, both for amore effective emission of extreme ultraviolet and soft X-ray radiationand for pseudo-spark switches with repetition rates into the kilohertzrange. An additional switching element is used between a capacitor bankand the electrodes in the plasma pinch, which is operated withspontaneous breakdown. The plasma is not in contact with the insulatorand should only reduce a wear of the insulators. The device, which is ofa comparatively complicated construction, however, fails to protect theelectrode surfaces sufficiently against erosion.

As is disclosed in DE-OS 101 39 677, a plasma pinch triggered by hollowcathodes, HCT pinch for short, can be operated on the left-hand branchof the Paschen curve without a switching element and thus renderspossible a low-induction, effective coupling of energy. FIG. 1 from thisdocument laid open to public inspection diagrammatically shows theconstruction of a pseudo-spark plasma switch for generating extremeultraviolet or soft X-ray radiation.

A hollow cathode (10) and an anode (12) together with the insulators(18) define a discharge space (22). A current pulse generator causesthis electrode system to generate a plasma (26) through electricdischarge. This current pulse generator is symbolized by a capacitorbank (20). The plasma (26) is ignited along an axis of symmetry (24)defined by openings (14, 16) of the two electrodes (10, 12).

To generate the plasma (26), a suitable discharge gas has previouslybeen introduced into the discharge space (22) at a pressure (p) whichtypically lies in a range from 1 to 100 Pa. A pulsed current flow of afew tens up to a maximum of 100 kA with pulse durations typicallybetween 10 and a few hundreds ns length brings a pinch plasma totemperatures (T) of a few tens of electron volts and to densities suchthat the discharge gas used is excited into an efficient emission ofradiation (28) in the desired spectral range, through ohmic heating andelectromagnetic compression. A low-ohmic channel in the space betweenthe electrodes is generated by charge carriers in the rear space of thehollow cathode (10). Such charge carriers may be generated in variousways. For example, a surface spark trigger, a highly dielectric trigger,a ferroelectric trigger, or the pre-ionization mentioned above arepreferred for use in the hollow electrode for the generation of chargecarriers such as, for example, electrons. A strong thermal load on theelectrodes (10, 12) is caused thereby mainly at the openings (14, 16)owing to the high pulse energies.

It is possible to influence the required ignition voltage and topredetermine the moment of the electric discharge in particular throughthe use of auxiliary electrodes as known from WO-A-01/01736. Suchauxiliary electrodes may alternatively be used for triggering, such thatthe capacitor bank (20) need not be charged up to the ignition voltage,but to a lower level. This, however, again generates the plasma in thehollow cathode that strongly erodes the electrode surface anddisadvantageously shortens electrode life.

The invention accordingly has for its object to provide a method and adevice for generating a plasma through electric discharge which resultin a substantially longer operational life or to a higher averageloading capacity of the electrodes with the use of technically simplemeans.

According to the invention, this object is achieved in a method of thekind mentioned in the opening paragraph in that a sacrificial substrateis provided at least at the evaporation spot, the boiling point of saidsubstrate during discharge operation lying below the melting point ofthe carrier material, such that charge carriers arising in the currentflow are mainly generated from the sacrificial substrate.

In this manner the low-melting sacrificial substrate is sacrificed tothe benefit of the matrix material so as to keep the electrode shapeconstant.

Since the current flow from an electrode surface into the plasma alwaysalso evaporates a portion of the surface material, the electrode shapeis usually changed, which has an adverse effect on the efficiency of theplasma formation. The size and position of the plasma are also changedthereby, so that these electrodes become useless for obtaining areproducible stable plasma. Usual electrodes are made of solid,electrically and thermally well-conducting materials which are suitablefor a low-loss current passage into the plasma on the one hand, and onthe other hand for a discharge of thermal energy from the plasma.

Preferably, the method is arranged such that the sacrificial substrateis supplied through the electrode to a surface that faces the electricdischarge.

The material losses necessary for enabling the current transport arebalanced such that the outer shape of the electrode remains intact for along period. Advantageously, the method is arranged such that thesacrificial substrate has a lower melting point than the electrodes. Theliquid sacrificial substrate then acts as a mobile phase which can betransported quickly and effectively onto the surface of an electrode.

In a further embodiment of the invention, the method is advantageouslyarranged such that the surface is wetted by the sacrificial substrate.This prevents a direct contact between the plasma and a matrix thatdefines the outer shape of the electrode. The surface facing theelectric discharge is continuously renewed by the transport of thesacrificial substrate induced by capillary forces.

A particularly advantageous embodiment of the invention is obtained whenthe discharge is operated at an average temperature of the electrodethat lies above the melting point of the sacrificial substrate. Thisaverage temperature then always lies below the melting point of thecarrier material that defines the outer shape of the electrode. Athermal load on the electrode is caused by an emission of radiation andhot particles such as, for example, ions from the plasma or a pulsatoryenergy of up to several tens J in an electric discharge. This isinsufficient for a thermally induced emission of electrons in sufficientquantities. On the surface of an electrode, preferably a cathode, theknown process of local overheating or spot formation accordingly takesplace, whereby electrode material is evaporated. The evaporatingelectrode material then usually provides the charge carriers, forexample electrons, necessary for the discharge to the plasma. Thesacrificial substrate wetting the surface of the electrode evaporateswhen its boiling point is exceeded, limits the erosion of the carriermaterial of the electrode, and in addition favors the spot formation inthe evolving vapor.

Preferably, the method of generating a plasma through electric dischargeis arranged such that the mass of the sacrificial substrate evaporatedby the discharge is supplemented from a reservoir. Losses occurring atthe surface of an electrode owing to the wetting sacrificial substrateare made good automatically through supplementation of sacrificialsubstrate by capillary forces. The carrier material here operates like awet sponge.

In a further embodiment of the invention it is provided that theevaporated sacrificial substrate is returned into a or the reservoirafter condensation. The sacrificial substrate wetting the matrix of thecarrier material can flow off immediately, so that the outer shape ofthe electrode according to the invention remains unchanged afterwards. Apollution of an optical system for, for example, EUV lithography byevaporating sacrificial substrate remains comparatively small, whichleads to a higher useful output.

A particularly advantageous method of generating a plasma throughelectric discharge is arranged such that the electric discharge isoperated on the left-hand branch of the Paschen curve at a given gaspressure. The choice of an operating point on the Paschen curve on theleft of the minimum renders it possible in particular to increase theradiant efficacy in the desired wavelength range such as, for example,extreme ultraviolet and soft X-ray radiation, and to define thecharacteristic of a pseudo-spark plasma switch more exactly.

A further advantage of the method may be that a gas is present betweenthe electrodes, which gas comprises at least one component thatgenerates the radiation. Xenon may be used for this, for example. Thehighly ionized xenon ions formed in the plasma pinch emit radiation at,for example, a wavelength of 13.5 nm. If a partial pressure of theradiation-emitting gas is chosen to be too high in the discharge space,however, the generated radiation will also be absorbed.

To increase the intensity of the generated radiation, the method ispreferably arranged such that a main ingredient of the gas istransparent to the emitted radiation. Helium, argon, or nitrogen may beused for this, for example, so as to adjust a gas pressure of typically1 to 100 Pa in the discharge space, thus defining an operating point onthe left-hand branch of the Paschen curve given a suitable electrodegeometry.

The quantity of sacrificed material in one pulse in the HCT pinchdischarge is lower by orders of magnitude than the gas quantity betweenthe electrodes achieving the gas discharge and contributing to theradiation emission. It is accordingly advantageous that substantiallymore sacrificial substrate is evaporated through a short-periodintroduction of additional energy before the discharge at least in thatlocation or those locations where the cathode spots or evaporation areasusually occur, for example by means of a laser pulse or electron beam.An energy of the additional laser pulse of approximately 50 mJ iscapable of generating a particle quantity of the sacrificial substratein a range of 10¹⁵ particles in the form of a vapor. The particlequantity of the sacrificial substrate vapor thus generated thencorresponds approximately to that of the discharge gas that is normallyused. As a result, the plasma pinch is mainly formed in the vapor, andthe properties of the vapor now define the radiation emission while theadvantages of the dimensional stability of the electrode carrier ormatrix material are retained. Thanks to the energy pulse that frees thevapor between the electrodes, it is possible in certain cases todispense with an additional gas all together. The electrode system isaccordingly initially in a vacuum (for example 10⁻⁶ mbar), i.e. very farto the left on the Paschen curve. It is not until the vapor is evolvedthat the discharge is generated and forms a pinch in the sacrificialsubstrate vapor.

The method is preferably arranged such that sacrificial substrates suchas tin, indium, gallium, lithium, gold, lanthanum, aluminum, and alloysthereof and/or chemical compounds thereof with other elements are used.The elements mentioned above and their salts, some of which boil atconsiderably lower temperatures, may be used in particular forgenerating extreme ultraviolet and/or soft X-ray radiation, and theliquidity range of the sacrificial substrate can be adapted to thematrix material.

According to the invention, furthermore, the object as regards a deviceof the kind mentioned in the opening paragraph is achieved by anarrangement which supplies a sacrificial substrate at least at theevaporation spot, the boiling point of said sacrificial substrate lyingbelow the melting point of the carrier material during dischargeoperation, such that charge carriers arising in the case of a flow ofcurrent can be generated mainly from the sacrificial substrate.

The electrode of the device according to the invention may be used inprinciple for any application based on a gas discharge. Its outer shapemay also be designed in any manner as desired such as, for example, inthe form of a cylinder or a hollow electrode.

A particularly advantageous device is obtained when a plasma can beformed along an axis of symmetry defined by openings in the dischargespace formed by at least two electrodes and at least one insulator whena defined ignition voltage is reached. This renders it possible, forexample, to generate a HCT pinch plasma with a defined spatial dimensionby spontaneous breakdown, at a comparatively large distance to thesurface of the discharge space. The thermal load on the electrodes andaccordingly the electrode erosion can be kept low thereby.

A further embodiment of the invention provides that the carrier materialis porous or has capillary-type channels. The additional sacrificialsubstrate then exits through the carrier material defining the outershape of the electrode, preferably at the surface that faces theelectric discharge.

The device is preferably designed such that the carrier material isconnected to at least one reservoir which contains the sacrificialsubstrate in liquid and/or gaseous form. The reservoir serves both forsupplementing the material losses at the surface of the electrodenecessarily following the discharge operation and for receivingsacrificial substrate that has condensed in cooler locations of thesurface of the discharge space, such that the outer shape of theelectrode is always retained. It is obviously also possible to supplythe sacrificial substrate in the solid state to the reservoir and/or thedischarge space, for example in the form of a wire.

In the embodiment of the device for generating the plasma as describedabove, it is useful when the carrier material is made from a refractivematerial, preferably a metal or a metal alloy, or from a ceramicmaterial. Obviously, the outer shape of the carrier material defining anelectrode may be formed from any temperature-resistant material.

A particularly advantageous device for generating a plasma isconstructed such that the carrier material on at least one of thesurfaces facing the plasma of one of the electrodes has a porous shapewhich is different from the porous shape of other portions of thecarrier material.

This renders it possible for the carrier material on the surface of anelectrode to have pores of different size. Suitable manufacturingprocesses are capable of making pores which compensate for local highlosses of sacrificial substrate, for example through absorption of amajor quantity of the sacrificial substrate, which high losses occur,for example, along or on the axis of symmetry of the plasma pinch,because this is where exposure to the high current flow is strongest.

It is alternatively possible and advantageous when the pore size withinthe carrier material is different, for example becomes smaller from theinside towards the surface. The capillary forces then advantageouslysupport the sacrificial substrate transport.

Without imposing any limitation on the general use of the device or themethod for the generation of a plasma through electric discharge forapplications based on gas discharges, an advantageous use is found inthe generation of radiation in the range of extreme ultraviolet and/orsoft X-ray radiation, in particular for EUV lithography.

The method and the device may also be used for controlling very highcurrent strengths, in particular for high-power switches.

Further features and advantages of the invention will become apparentfrom he ensuing description of five embodiments and from the drawings towhich reference is made. In the drawings:

FIG. 1 is a diagram of an electrode geometry according to the prior art;

FIG. 2 shows an electrode with a sacrificial substrate that can beadditionally supplied in a first embodiment;

FIG. 3 diagrammatically shows an electrode cross-section in a secondembodiment;

FIG. 4 diagrammatically shows an electrode provided with an additionalsacrificial substrate during discharge operation in a third embodiment;

FIG. 5 diagrammatically shows an electrode cross-section with anadditionally provided sacrificial substrate and an electrode surfacetemperature distribution during operation of a fourth embodiment; and

FIG. 6 diagrammatically shows an electrode geometry with capillary-typechannels in a fifth embodiment.

Identical reference symbols always relate to the same constructionalfeatures and relate to FIGS. 2 to 6, unless stated to the contrary.

The operating principle according to the invention of a first embodimentof a device with a self-regenerating electrode 10 is described inparticular with reference to FIG. 2. The electrode 10 is formed from aporous carrier material 30 in whose internal spaces a sacrificialsubstrate 38 with a lower melting point than the porous carrier material30 is provided. The sacrificial substrate 38 is present in liquid formin a reservoir 24 and is in communication with a surface 36 (FIG. 3)facing the electric discharge via a passage 32. The liquid sacrificialsubstrate 38 preferably has the property of wetting the porous carriermaterial 30.

FIG. 3 shows a second embodiment of a device according to the inventionwith a renewable electrode 10 in a diagrammatic cross-section. Theporous carrier material 30 is constructed as a matrix 40 obtained bysintering of metal bodies, preferably refractive metals such as tungstenor molybdenum. The metal bodies may be varied in shape and size suchthat a suitable sintering process is capable of generatingcorrespondingly dimensioned pores on the surface 36 or in theintervening spaces and channels 48 in the electrode 10. Obviously, theporous carrier material 30 may alternatively be a ceramic material. Theintervening spaces in the matrix 40 are filled with the liquidsacrificial substrate 38 in the electrode 10 according to the inventionduring operation. The melting and boiling points of the sacrificialsubstrate 38 are chosen such that they are lower than the melting pointof the matrix 40. If the sacrificial substrate 38 wets the matrix 40,naturally occurring capillary forces in the pores exert a suction effectfrom the reservoir 34 into the porous carrier material 30. Thissponge-like property of the porous carrier material 30 leads to acontinuous supplementation of the liquid sacrificial substrate 38 intothe surface 36 during the discharge operation, thus compensating for thenormally occurring detritus of electrode material.

FIG. 4 is a diagrammatic cross-sectional view of a third embodiment of adevice in discharge operation. A discharge here heats the surface 36 ofan electrode 10 by means of the flow of current 42 so strongly that theliquid sacrificial substrate 38 partly evaporates from the surface 36,thus forming a vapor 44. Since the sacrificial substrate 38 wets thematrix 40, the plasma 26 will come into contact with the sacrificialsubstrate 38 only. It is not absolutely necessary here for the surface36 of the electrode 10 to be fully wetted by the sacrificial substrate38. The sacrificial substrate 38 is capable of taking over the currenttransport from the electrode 10 also if it is only present in the regionof the pores. The sacrificial substrate is then additionally provided tothe surface 36 of the electrode 10 through this electrode 10 by acapillary force 46, as required, such that the contour of the matrix 40and accordingly the outer shape of the electrode 10 remain unchanged.

A fourth embodiment is shown in FIG. 5. The sacrificial substrate 38evaporates from a surface 36 of a matrix 40 upon ignition of a plasma 26when a temperature T1 of an electrode spot under formation reaches theboiling point of the sacrificial substrate 38. The supplementary supplyof sacrificial substrate 38 limits the thermal load on the matrix 40 toT1, because the energy applied to the surface 36 by the formation of theplasma 26 is removed in the form of evaporation enthalpy of thesacrificial substrate 38. The additionally evaporating sacrificialsubstrate 38 cools the surfaces 36 slightly during this and forms avapor 50 which moves in all spatial directions owing to convection. Thevapor of the sacrificial substrate 38, however, is capable of condensingfor the major portion in the cooler locations of the electrode 10outside the spot and is returned through the pores to the matrixmaterial 30 again. Cooler regions of the surface 36 lying outside theplasma contact are reached by collisions with the surface 36 in regionshaving a temperature T2 below the boiling point T1 of the sacrificialsubstrate 38, which regions absorb the thermal energy stored in thevapor 50. The sacrificial substrate 38 is condensed as a result of thisand is returned. This may take place, for example, by means of thecapillary forces 36 in the porous carrier material 30 mentioned above.The average operating temperature then always lies above the meltingpoint of the sacrificial substrate 38 and below the melting point of thematrix 40. It is possible by means of an arrangement not shown here, forexample by means of a laser pulse or an electron beam, to supplyadditional energy for a short period before the discharge at least inthose locations where cathode spots or evaporation spots usually occurso as to evaporate additional sacrificial substrate 38. The particlemass of the sacrificial substrate 38 thus generated, which may be, forexample, tin, indium, gallium, lithium, and alloys and/or chemicalcompounds with other elements thereof, in this case correspondsapproximately to the mass of the discharge gas used for generating EUVand/or soft X-ray radiation.

A particularly advantageous embodiment of a device according to theinvention is shown in FIG. 6. In this sixth embodiment, an electrode 10has a first opening 14 which is coaxial with the axis of symmetry 24 ofan electric discharge. The electrode 10 comprises besides a carriermaterial 30 at least one reservoir 34 which contains a liquid and/orgaseous sacrificial substrate 38, and capillary-type channels 48extending to the surface 36. The surface tension of the liquidsacrificial substrate 38 issuing from the surface 36 gives rise toplanarly bounded regions of a wetted surface 52 which protects thecarrier material 30 against erosion in the discharge operation. Asuitable arrangement of the capillary-type channels 48 in the carriermaterial 30 is capable of achieving a suitable supply of sacrificialsubstrate 38 in accordance with the requirements. The surface 36, andthus the electrode 10, is continuously regenerated. The sacrificialsubstrate 38 may alternatively be supplied in wire form to the reservoir34 and/or the surface 36, or the discharge space 22 (shown in FIG. 1,not in FIG. 6), as required.

The invention provides a method and a device for the generation of aplasma through electric discharge which is stable in shape and which maybe used in particular as a source of radiation in the range of extremeultraviolet and/or soft X-ray radiation, or as a pseudo-spark plasmaswitch.

LIST OF REFERENCE SYMBOLS

-   10 electrode I-   12 electrode II-   14 first opening-   16 second opening-   18 insulator-   20 capacitor bank-   22 discharge space-   24 axis of symmetry-   26 plasma-   28 radiation-   30 carrier material, matrix material-   32 feed passage-   34 reservoir-   36 surface-   38 sacrificial substrate-   40 matrix-   42 current flow-   44 substrate vapor-   46 capillary force-   48 channel-   50 vapor-   52 wetted surface-   p gas pressure-   T, T1, T2 temperatures-   U ignition voltage

1. A method for the generation of a plasma through electric discharge ina discharge space which contains at least two electrodes, at least oneof which is constructed from a matrix material or carrier material, suchthat an erosion-susceptible region with an evaporation spot is formed atleast by the current flow, characterized in that a sacrificial substrate(38) is provided at least at the evaporation spot, the boiling point ofsaid sacrificial substrate (38) during discharge operation lying belowthe melting point of the carrier material (30), such that chargecarriers arising in the current flow are mainly generated from thesacrificial substrate (38).
 2. A method as claimed in claim 1,characterized in that the sacrificial substrate (38) is supplied throughthe electrode (10) to a surface (36) that faces the electric discharge.3. A method as claimed in claim 1, characterized in that said surface(36) is wetted by the sacrificial substrate (38).
 4. A method as claimedin claim 1, characterized in that the discharge is operated at anaverage temperature (T) of the electrodes (10) that lies above themelting point of the sacrificial substrate (38).
 5. A method as claimedin claim 1, characterized in that the mass of the sacrificial substrate(38) evaporated by the discharge is supplemented from a reservoir (34).6. A method as claimed in claim 1, characterized in that the evaporatedsacrificial substrate (38) is returned into a or the reservoir (34)after condensation.
 7. A method as claimed in claim 1, characterized inthat the electric discharge is operated on the left-hand branch of thePaschen curve at a given gas pressure (p).
 8. A method as claimed inclaim 1, characterized in that a gas is present between the electrodes(10, 12), which gas comprises at least one component that generatesradiation (28).
 9. A method as claimed in claim 8, characterized in thata main ingredient of the gas is transparent to the emitted radiation(28).
 10. A method as claimed in claim 1, characterized in thatsubstantially more sacrificial substrate is evaporated through ashort-period introduction of additional energy before the discharge atleast in that location or those locations where the cathode spots orevaporation areas usually occur, for example by means of a laser pulseor electron beam.
 11. A method as claimed in claim 1, characterized inthat sacrificial substrates (38) such as tin, indium, gallium, lithium,gold, lanthanum, aluminum, and alloys thereof and/or chemical compoundsthereof with other elements are used.
 12. A device for generating aplasma through electric discharge, comprising a discharge space (22)having at least two electrodes, of which at least one is constructedfrom a matrix material or carrier material such that anerosion-susceptible region with an evaporation spot is formed at leastowing to the flow of current, characterized by an arrangement whichsupplies a sacrificial substrate (38) at least at the evaporation spot,the boiling point of said sacrificial substrate (38) lying below themelting point of the carrier material (30) during discharge operation,such that charge carriers arising in the case of a flow of current canbe generated mainly from the sacrificial substrate (38).
 13. A device asclaimed in claim 12, characterized in that a plasma (26) can be formedalong an axis of symmetry (24) defined by openings (14, 16) in thedischarge space, which is formed by at least two electrodes (10, 12) andat least one insulator (18), when a defined ignition voltage is reached.14. A device as claimed in claim 12, characterized in that the carriermaterial (30) is porous or has capillary-type channels (48).
 15. Adevice as claimed in claim 12, characterized in that the carriermaterial (30) is connected to at least one reservoir (34) which containsthe sacrificial substrate (38) in liquid and/or gaseous form.
 16. Adevice as claimed in claim 12, characterized in that the carriermaterial (30) is formed by a refractive material, preferably a metal ora metal alloy, or from a ceramic material.
 17. A device as claimed inclaim 12, characterized in that the carrier material (30) has a porousshape on at least one of the plasma-facing surfaces of one of theelectrodes (10), which shape is different from the porous shape of otherportions of the carrier material (30).
 18. The use of the method and/orthe device for the generation of plasma as claimed in claim 1 for thegeneration of radiation in the range of extreme ultraviolet and/or softX-ray radiation, in particular for EUV lithography.
 19. The use of themethod and/or the device for the generation of plasma (26) as claimed inclaim 1 for controlling very high current strengths, in particular forhigh-power switches.